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What transmission to plan on using?

ChallengerGary

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Starting the planning process for an upcoming project and am confused about which transmission I should look into using.

The car is a 71 Challenger, /6 with factory 3-speed manual. The engine I am considering buying (if they guy still has it once I sell either of my 340 Dusters) is a 2018 5.7 that has upgraded cam, springs, lifters and injectors. It Dyno'd at mid 400hp range to the wheels in the 2018 Challenger it was pulled from (guy upgraded to a 6.2 and is putting a whipple on it too). I plan on driving the daylights out of the car once I complete it. It WILL NOT be a trailer queen and as such I am thinking that something with OD. I also plan on doing a bunch of chassis stiffening so the car will be more of a resto-mod in the end. Not opposed to rowing gears but not 100% necessary either. What transmission would give me what I am looking for without braking the bank? I don't mind modifying the hump so that is not a limiting factor
 

scar426

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Your decision will be based primarily on what engine management/wiring harness you decide to use. The MOPAR harness is designed for standard transmission, and aftermarket harness from someone like HOTWIREAUTO.com can be had for either the 545RFE, NAG-1 or 8spd autos. HOWEVER...... the NAG1 and 8 spd require a lot more "Stuff" (electronics, abs module, shifter, etc..) to make them work, the 545RFE does not. I prefer and have used a 545RFE on my two builds...5.7l in my 47 Hudson cpe and a 6.4l in my 48 Panel van, both work great with zero issues and a simple Lokar shifter.
 

Katfish

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I put a 518 behind my 340, and it was the best thing I ever did. Having OD made the car so much more enjoyable to drive. I'm in the middle of swapping in a 5.7 and hope to have it done soon. Staying with the 518, we'll see how it goes.
 

scar426

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He did say without breaking the bank, lol... BTW my 545rfe for the 5.7l came with the motor ($3k for the whole setup), so no added cost, the 6.4l setup, I bought a used one for $550 and had it rebuilt for $1000, so.......fairly cheap. Oh and the truck CPUs have the TCM integrated into it already, so literally plug and play, add a shifter couple $100 and good to go.
 

heminut

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I put a 518 behind my 340, and it was the best thing I ever did. Having OD made the car so much more enjoyable to drive. I'm in the middle of swapping in a 5.7 and hope to have it done soon. Staying with the 518, we'll see how it goes.
This right here!^^^^ The 518 will hold up just fine. Minimal mods and an economical swap.
 

SFEbody

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I am using the HP-70 8 speed auto from a 2017 charger. The 8 speed with 3.23 gears will pull about 1900-RPM on the freeway at 70MPH. HotwireAuto has the complete hookup for that trans and the 5.7 Hemi
 

ChallengerGary

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Ok - so it sounds like the A518 is the most economical route depending on how much I have to spend on the actual transmission. HotWireAuto looks like a good choice for the harness.
 

Katfish

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If I had to do over, I might consider a GM tranny, supposed to be smaller and easier to control. The 518 does require some money and effort to retain the factory kick down functionality.
 

scar426

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I can understand using a 518 IF....IF you are going to stay with a traditional small block i.e. 318, 340, 360. But since as you mentioned you're looking at installing a modern 5.7L Hemi, then WHY would you want to take a step back and install an older style/functional transmission. Get the harness from Chris at HOTWIREAUTO.com with a computer that will run the 545RFE (plug and play electronically) and just add an appropriate automatic shifter. No kickdown anything required, so special anything. The wheel was already recreated in this instance, why try to complicate it and re-recreate it. Trust me, it is NOT going to be cheaper or easier to use a 518 vs a 545RFE in this case. (As a side note, up until the NAG1 all the newer trannies (518, 45RFE, 545RFE) are a derivative of the 727 anyways.) AND that's assuming you can find a 518 to use in the first place (where I'm located you can't find any.) Just my two cents, do what ya want/like. I've only done 2 modern hemi swaps into older vehicles and this is what i have found to be true.:thumbsup: Oh and another note, the modern hemi/545RFE trans combo can be mounted with the starter on either side if clearance is an issue.
 

SFEbody

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Her is what I had to cut on the HP-70. You will notice i removed the 4 speed tunnel, but have since put one back just in case i want to convert it down the road to manual.

Tunnel.jpeg
 
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